The present invention relates to a universal compact disc (CD) player that allows either portable battery powered or standard AC powered operation to decode any digital audio file from a CD.
Today, all CD players allow decoding (playing) of only the standard CDDA digital format, which is used by all music record manufacturers ("labels").
However, in recent years, various compression schemes and digital delivery of audio files have been designed to accommodate efficient music delivery over digital networks such as the Internet with concomitant savings in storage space on CDs, personal computer hard drives, etc. The advantage of such compression schemes may be illustrated in the following table, which shows the time needed to transmit a high-quality, three-minute audio file:
______________________________________ Maximum modem Compression Year of First Use speed (kbps) Transmission Time ______________________________________ 2x 1991 2.4 14 hrs 11x 1997 28.8 13 min. 16x 2003 (est.) 400.0 38 sec. ______________________________________
As can be seen, the availability of highly efficient compression schemes and very high bandwidth transmission facilities will result in the ability for an individual to download a high-quality musical piece in a very acceptable time period. Therefore, it is predicted that electronic sales of music and entertainment products via the Internet, proprietary online services, CD-Rom, interactive television, kiosks and screen phones will quintuple to $186 million by the year 2000 (conservatively) or to as much as $1.3 billion, or 10 percent of the industry total.
There is therefore a fierce battle over which compression scheme will be adapted as a standard for the music industry. At present, there are at least four agencies claiming to be the mainstream of the music industries. In addition, a number of studies are under way on new compression schemes. The four types of compression schemes currently dominating the market place are:
(1) Moving Picture Experts Group (MPEG): a standard compression scheme for coding of moving pictures and associated audio for digital storage media at up to 1.5 megabits/sec (Mbps). This is an international standard of the International Organisation for Standardisation (ISO), in 5 parts (ISO/IEC 11172-1 through-5). MPEG players (see below) are freely distributed over the Internet to millions of computer users. PA1 (2) Real Audio: a compression scheme for coding both video and audio for streaming transmission and download over the Internet. This compression scheme was designed by Progressive Networks (now RealNetworks) and has perhaps the largest market share of any of the proprietary schemes. RealNetworks freely distributes a player over the Internet to anyone who wants it. PA1 (3) Liquid Audio: another proprietary compression scheme for audio and associated lyrics, credits and artwork contained in a single audio file. This compression scheme also uses Dolby Digital encoding to increase the quality of the audio. Like RealNetworks, Liquid Audio provides a free player. PA1 (4) A2b: another proprietary transmission scheme developed by AT&T. PA1 (1) a player, which is required to listen to streaming audio or to play any digital file that resides on a hard disk. The player decompresses the music files, which were previously compressed; and PA1 (2) a decoder to decompress and decode the compressed audio.
Generally speaking, all of these compression schemes have the following components:
A great number of encoders exist (even within a given compression scheme such as MPEG). However, all encoders involve some mathematical algorithm which examines the audio stream and removes "redundant" information which cannot be distinguished by the human ear. For example, an audio CD holds about 60 to 72 minutes of 16 bit, 44.1 kHz raw audio data, for a total of about 650 Mbytes of data. The classic way to reduce the size of the data is to reduce the sampling rate from 44.1 kHz to 22 kHz, or to convert 16 bit samples to 8 bit samples. Unfortunately, a simple method such as this results in losing about half the quality of the audio.
Encoders involve sophisticated mathematical processing to reduce the size of the audio file without a one-for-one reduction in quality. Based on research of human perception, the encoder decides what information is elementary and what can be stripped. For example, in MPEG the audio encoder removes a weaker signal that follows a strong signal, because the weaker signal would not be recognized by the brain even if allowed to pass to the ear. The higher the compression, the more information is stripped, and the more likely that the listener will perceive a difference in audio quality.
Decoders use sophisticated mathematical processing to decompress the encoded audio file. The sophisticated mathematical processing used by a decoder may be carried out by any computer. Today, thousands of people are downloading MPEG files over the Internet and decoding them using free players which use the microprocessor of the personal computer, in conjunction with a "sound card", to implement the decoder. But these people, and others, also want the ability to play these compressed files in a portable device. No flexible means of compressed music playback without the use of a computer exists at present.
There is therefore a need for a universal CD player that can decode and play a compressed audio file that was encoded by any encoder. The present invention provides such a solution through the use of digital signal processing (DSP) technology integrated into a CD player's decoder.
In another aspect of the present invention, there is provided a universal compressed audio player that can decode and play a compressed audio file that was encoded by any encoder. The compressed audo file can reside in any storage accessible to the player, including internal random access memory (RAM) or removable memory such as a memory card.